The present invention relates to an apparatus providing a pattern evaluation of a sample, for example, a substrate having a pattern with a minimum line width not greater than 0.1 μm with a high throughput, and also to an evaluation method of a pattern by using the same apparatus.
The present invention further relates to a pattern evaluation method that provides an evaluation, such as a defect inspection for a chip having a pattern with a minimum line width not greater than 0.1 μm in an inexpensive manner, with a reduced foot print as well as with a high throughput.
The present invention further relates to a method for manufacturing a device by using said electron beam apparatus or pattern evaluation method.
In the evaluation of a pattern formed on a substrate by using an electron beam, it has been conventionally suggested to use a multi-beam in order to improve the throughput. Such suggestions may be categorized roughly into two methods: a method of using a multi-beam having a plurality of optical axes; and a method of forming a multi-beam on spots spaced equally from a single optical axis.
The former method, or the method of using the multi-beam having a plurality of optical axes, however, has a problem that a need for making a large number of electron optical lens columns leads to an increase in the entire cost of the apparatus, and a further problem that it is impossible to arrange a large number of optical axes on a single substrate, or on a wafer.
On the other hand, the latter method, or the method of forming the multi-beam on the spots spaced equally from the single optical axis also has a problem that the beam to be formed away from the optical axis increases an aberration in an optical system and does not allow an increase in intensity of the beams. In a trial to address these problems, an attempt to arrange more beams in the locations quite close to the optical axis caused another problem that secondary electrons generated from respective points scanned by the multi-beam overlap with one another due to the aberration in the optical system, while another attempt to extend a space between beams, which allows an individual detection, aiming at preventing the above problem of overlapping, has adversely prohibited producing a large number of multi-beams. Further, the electron beam apparatus according to the prior art typically has a problem that the length of a secondary optical system is rather longer.
More specifically, the apparatus according to the prior art employs a single step of objective lens 4 for focusing a primary electron beam 2 after the beam has passed through a reducing lens 1 onto a sample surface 3, as illustrated in FIG. 10. In an operation of this apparatus, if a landing energy of the primary electrons is large, an excitation voltage of the objective lens 4 will be increased, so that the secondary electrons 5 will form a secondary electron image 6 immediately above the objective lens 4 with a large half-angular aperture αi, as illustrated, which could fall out of lens, unless an aperture size of the lens 8 is made larger. From this point of view, it is necessary to enlarge the aperture size of the lens 8, which in turn, could disadvantageously lead to a drawback of the increased aberration. Further, since a lens of a second optical system is not allowed to be positioned close to the objective lens, the lens having an object point in a distance serving as a magnifying lens, is required to make its image point defined at a further distant location, which disadvantageously makes an entire length of the secondary optical system much longer. It is to be noted that in the drawing, reference numeral 9 designates an E×B separator serving for separating the secondary electrons from the primary optical system.
The present invention has been made in the light of the above problems, and accordingly a first subject to be addressed by the present invention is to provide an electron beam apparatus and an evaluation method of a pattern by using said apparatus, which can be manufactured at low cost and which can reduce the aberration in the optical system for detecting the secondary electrons and to allow the large number of multi-beams to be formed in the vicinity of the single optical axis.
In the art, there has been known a method for providing an evaluation such as a defect inspection for a pattern formed on a chip by using an electron beam apparatus (see, for example, Japanese Patent Laid-open Publication No. Hei7-249393). In the practice according to the prior art, such an evaluation apparatus comprising a memory capable of storing the images for at least two chips is used, wherein an entire pattern formed on a single chip is stored, and said pattern is compared with the entire pattern formed on another chip so as to detect a defect. Further, a probe used for the defect detection is of a type using a single electron beam.
However, the prior art method has a problem that the memory for storing the image data should be extremely large in size and yet a further problem that using only a single beam as the probe results in an extremely low throughput.
Accordingly, a second object of the present invention is to provide a pattern evaluation method that can work effectively with a small sized memory for storing the image data in the evaluation apparatus.
Another object of the present invention is to provide a method which can increase a throughput by using a multi-beam to make the pattern evaluation.
Yet another object of the present invention is to provide a manufacturing method of a device, in which an apparatus or a method as specified above is used to evaluate a sample in the course of processing.